The earliest instances of relatively prolonged cardiac stimulation, namely cardiac pacing, of a patient's heart was effected through implanted cardiac leads attached to the heart muscle at distal electrode ends and extended through an incision in the patient's skin. Initially, cardiac pacing was employed during post-operative recovery from cardiac surgery, and the attachment to the heart was made to the epicardium during the surgical procedure. To effect unipolar pacing of the heart, a single such implantable pacing lead was employed in conjunction with a subcutaneously implanted or skin surface attached return electrode coupled to an external lead conductor. To effect bipolar pacing of the heart, two such implantable pacing leads were implanted with the electrode ends implanted a distance apart. Initially, the attachment mechanism typically required a second surgical procedure to remove the distal electrode(s) and the pacing lead(s).
The attachment of the proximal ends of the lead conductors to the temporary cardiac pacemaker connector elements was initially effected by simply stripping insulation from the proximal conductor ends, inserting the bare conductor ends around or through transverse openings in threaded posts, and tightening down thumb nuts. Later, finished connector pins were formed at the proximal connector ends of the lead bodies that could be inserted into end openings of the thumb nuts and connector posts.
Implantable pacing leads evolved into permanent, unipolar and bipolar, endocardial and epicardial, pacing leads for chronic implantation in a patient and with proximal electrical connector assemblies connected with connector elements of a totally implanted, cardiac pacemaker pulse generator. To withstand stress, implantable pacing lead conductors were formed of coiled wire and inserted within an insulative lead body lumen, thereby providing a coiled wire lumen that was sized to receive a stiffening stylet wire to assist transvenous implantation of endocardial pacing leads. The proximal end of the coiled wire conductor was attached to a tubular connector pin at the terminus of the lead connector end shaped to be received in the connector assembly of the implantable pacemaker pulse generator. In the case of endocardial permanent pacing leads, the connector pin was formed with a lumen therein aligned with the coiled wire lumen so that the stiffening stylet wire could be inserted down the length of the lead body, used during the transvenous introduction, and withdrawn after placement of the distal electrode was achieved. Many of these features are employed in current permanent pacing leads.
More recently, bipolar and multi-polar permanently implantable pacing leads and leads for use in pacing and cardioversion/defibrillation (collectively referred to as permanent implantable cardiac leads) have been developed using coaxially arranged, coiled wire conductors and/or parallel-wound, multi-filar coiled wire conductors. In the case of endocardial cardiac leads, the stylet wire lumen is employed to receive the stiffening stylet wire for implantation as described above. The proximal connector end assemblies are formed with at least two spaced apart lead connector elements arranged in-line from a proximal lead connector pin to at least one more distally located ring-shaped element or lead connector ring. Typical bipolar in-line lead connector assemblies for multi-filar, coiled wire conductors are shown, for example, in commonly assigned U.S. Pat. Nos. 4,944,088 and 4,951,687 and 5,007,435, respectively, incorporated herein by reference.
Different manufacturers have produced implantable cardiac leads with lead connector end assemblies that match the connector block terminals of implantable medical devices of the same manufacturer. In recent years, one dimensional pacemaker connector standard has been made implemented, namely the low profile connector "IS-1" standard (ISO 5841-3:1992(E)) for bipolar in-line and unipolar lead connector end assemblies. Other permanent, bipolar, in-line, cardiac lead connector end assemblies conform dimensionally with the MEDTRONIC 3.2 mm low profile connector standard. Certain permanent unipolar cardiac lead connector end assemblies conform dimensionally with the MEDTRONIC 5 mm connector standard.
Unipolar and bipolar, temporary endocardial pacing leads and temporary epicardial heart wires were also developed for implantation of the distal electrode(s) thereof in contact with the endocardium or sutured through the epicardium of the hearts of hospitalized patients. The lead body size of these temporary pacing leads and heart wires has typically been smaller than that of permanent cardiac leads because of the absence of an internal wire coil lumen for receiving a stiffening stylet wire. Still, in the case of bipolar temporary pacing leads and heart wires, either a lead connector pin and ring set having comparable separations apart to those of permanent cardiac leads or bifurcated lead connector assemblies are employed providing a pair of lead connector pins. Exemplary temporary bipolar pacing leads include the MEDTRONIC.RTM. TEMPTRON temporary pacing leads having a uniform diameter, in-line, connector pin and ring assembly. Exemplary heart wires include the MEDTRONIC.RTM. Model Nos. 6491, 6492, 6494 and 6500 unipolar heart wires and the Model 6495 bipolar heart wire as described in commonly assigned U.S. Pat. No. 4,341,226, incorporated herein by reference.
During a hospitalization, a heart wire or temporary pacing lead of these types may be implanted to allow monitoring and demand pacing of the heart as the patient recovers from cardiac surgery or another condition. In addition, it may be necessary at times to connect the proximal connector end of a permanent cardiac lead already implanted in a patient to a temporary external pacemaker. The proximal connector end assemblies in each case are attached, for example, to external medical device connector elements of MEDTRONIC.RTM. Model Nos. 5348 or 5388 external single chamber or dual chamber cardiac pacemakers. The external medical device connector elements of such external cardiac pacemakers can constitute either spaced RCA type female sockets or a shrouded connector housing that are not compatible with cardiac lead connector end assemblies.
Therefore, when a bipolar heart wire or permanent or temporary pacing lead is to be connected, it is necessary to use a further "patient cable" adaptor to complete the connection. The MEDTRONIC.RTM. Model 5433A/V or the Model 5832/S reusable safety cables are employed to make the connection between the temporary pacemaker and the proximal connector ends of the heart wire or temporary pacing lead. Alternatively, the MEDTRONIC.RTM. Model 5455/S or the Model 5833/S disposable cable is employed to make the connection between the temporary pacemaker and the proximal connector ends of a temporary pacing lead.
A similar situation arises during a surgical implantation of a pacemaker or pacemaker-cardioverter-defibrillator including a permanent cardiac lead or lead system or the replacement connection of a implantable pulse generator of one of these types with a pre-existing permanent cardiac lead or lead system. During or after implantation of the implantable cardiac lead(s), an external pacing system analyzer, e.g., the MEDTRONIC.RTM. Model No. 5311B PSA, is attached to the proximal lead connector end assembly accessible through the incision to assess the performance of the system. Again, the Model 5311B connector elements are not compatible with the lead connector end elements for safety reasons. It is necessary to use either a disposable or a reusable "surgical cable" adaptor to complete the connection. Examples include the MEDTRONIC.RTM. Model 5410/S reusable surgical cable and the combination of the MEDTRONIC.RTM. Model 5411/S reusable adaptor and Model 5455/S disposable surgical cable.
Some of the above-identified patient and surgical cable adaptors constitute simply a connector assembly at one end that is compatible with the PSA or temporary pacemaker terminals, an external lead body enclosing the external lead conductors, and lead connector element connectors at the other end. Typically, two to four conductors are included in the lead body, and a set of two or four alligator clips are provided at the other ends for attachment to the lead connector ring and pin of one or two implantable cardiac leads.
Other, typically reusable patient and surgical cables employ a mechanism for receiving the proximal connector ends of the heart wire, temporary pacing lead or permanent cardiac lead. For example, either RCA type female sockets are used or a dual thumb screw attachment mechanism is used in the above-referenced MEDTRONIC.RTM. Model 5832/S and Model 5433A/V reusable patient cables, respectively.
Commonly assigned U.S. Pat. Nos. 4,245,642 and 4,466,441 disclose medical lead adaptors of the latter type wherein lead connector end assemblies are insertable into sockets of a housing to make electrical contact with a single or two electrical contacts spaced apart therein to receive bifurcated bipolar, in-line bipolar, or unipolar lead connector rings and/or pins. The attachment is effected by tightening down thumb screws to prevent the connector end assemblies from slipping out of the socket openings of the housing in each case. It is not possible to make an attachment with a permanent pacing lead having a stylet wire fitted within the lead lumen and projecting out proximally through the connector pin . This case can only be accommodated by the use of alligator clips that attach across the connector rings and pins.
Such an attachment is not as secure and electrically isolated as would be desirable. It is undesirable to either lose the connection or to allow an electrical static discharge or other shock or impulse to reach the heart through the exposed lead connector ends. At present, it is necessary to loop and tape the assembled adaptor lead and implantable lead body against the patient's body and also place tape over the alligator clips.
At times, it has been observed that the careless use of alligator clips can damage the insulation sheathes adjacent to the lead connector end ring or connector pin s. In IS-1 leads, damage to the insulating sheath and the seal rings on either side of the connector ring has been observed due to movement of the jaws of the alligator clips.